Scratch resistant clear coats: development of new testing methods for improved coatings

More and more car manufacturers are now demanding clear coats with improved scratch resistance from their paint suppliers. Some motor companies have developed their own tests, some have chosen a test developed by a paint supplier and others are still looking for their optimum test. The opinion prevails that there should be one test which covers all aspects of realistic damage. However, microscopic photographs and reflow experiments show that two kinds of scratches occur in reality, abrasive as well as non-abrasive, renewable ones. Different standard clear coat systems have different sensitivities to both scratch types. In the scratch tests the rating of the clear coats is divergent, because the ratio of both sorts of scratches differs. We have developed a set of two tests, where each test mainly generates one scratch type. These tests, together with physico-chemical measurements (glass transition onset temperature T g , laser optical profile scanning, indentation depths) lead to a deeper insight into scratch phenomena. One way to develop a clear coat which is resistant against all kinds of scratching damage is described.